Abstract: Using a continuous-wave type-II optical parametric oscillator below
threshold, we have demonstrated a novel source of heralded single-photons with
high-fidelity. The generated state is characterized by homodyne detection and
exhibits a 79% fidelity with a single-photon Fock state (91% after correction
of detection loss). The low admixture of vacuum and the well-defined
spatiotemporal mode are critical requirements for their subsequent use in
quantum information processing.